1. Field of the Invention
The present invention relates to an electrical connector, and particularly to an electrical connector having stand-offs for securely mounting fusible elements of the connector onto a printed circuit board.
2. Description of the Related Art
Ball Grid Array (BGA) sockets are widely used for electrically connecting an IC package, such as a Center Processing Unit (CPU) package to a circuit substrate, such as a PC board. A typical BGA Socket includes an insulative base defining a number of cavities therethrough, a number of conductive contacts received in corresponding cavities of the base, a number of solder balls attached to corresponding conductive contacts prior to the BGA socket being mounted to a PC board and a cover movably attached onto the base.
The cover defines a number of through-holes in accordance with the cavities of the base so that conductive pins of the CPU package may pass through the cover to engage with the corresponding conductive contacts in the base. When mount the BGA socket onto the PC board, the BGA socket connector is located on the PC board such that each solder ball is in accordance with a corresponding solder pad on the PC board. When heated, the solder balls melt and connect the corresponding solder pads. After cooled and frozen, the solder balls each combine with a corresponding solder pad and establish an electrical connection therebetween.
A typical issue existing in BGA socket is that, when heated, the solder balls melt and may be unable to support the base and the cover thereby being crashed by the base and the cover. After cooled, the adjacent solder balls interconnect each other, which results short circuit between the adjacent conductive pins of the CPU package. A first solution for this issue is to improve the material of solder balls. The solder balls each include a core whose melting point is a little higher than the temperature that the solder balls are heated and a mask enclosing the core whose melting point is a little lower than the temperature that the solder balls are heated. When the solder balls are heated, only the masks melt to combine corresponding solder pads on the PC board, and the cores are hard enough to support the base and the cover. A second solution for the above issue is to provide multiple stand-offs on a mounting surface of the base or the cover, which support the base and the cover and release the solder balls from the burden. The stand-offs are typically located at outer sides of the connector. U.S. Pat. Nos. 6,152,756 and 6,042,413, both issued to Hon Hai Precision Ind. Co. Ltd., disclose two types of such connectors.
Referring to FIGS. 4-6, a conventional BGA socket 1 includes an insulative base 11 receiving a plurality of conductive contacts 112 therein, a cover 13 movably attached onto the base 11 and a driver 14 located between the base 11 and the cover 13 for driving the cover 13 relative to the base 11. Each contact 112 has a solder ball 114 downwardly extending beyond a mounting surface 111 of the base 11 for mounting to a corresponding solder pad 116 on a printed circuit board (PCB) 20. The base 11 provides several stand-offs 117, 118 at outer sides thereof to support the connector 1 when the connector 1 is mounted onto the PCB 20. The base 11 and the cover 13 are manufactured by injecting plastic material into dies. So, the base 11 and the cover 13 may warp after they are released from the dies because of inner stress or when the connector 1 is mounted onto the PCB 20 because of warpage.
The connector 1 may warp upwardly that a center of the connector 1 spaces a larger distance from the PCB 20 than its surround. The solder balls 114 residing at the center of the connector may not be mounted onto corresponding solder pads 116 on the PCB 20, thereby contacts 112 residing at the center of the connector 1 are disconnected from the corresponding solder pads 116. On the other side, the connector 1 may warp downwardly that the center of the connector 1 spaces a smaller distance from the PCB 20 than its surround. When the connector 1 is mounted onto the PCB 20, the solder balls 114 residing at the center of the connector 1 may be crashed by the connector 1 and interconnect with adjacent solder balls 114, thereby inducing short circuits between these solder balls 114. Hence, an improved electrical connector is required to overcome the disadvantages of the prior art.
A first objective of the present invention is to provide an electronic device including a printed circuit board and an electrical connector that are able to be securely mounted onto the printed circuit board.
A second objective of the present invention is to provide an electrical connector having improved stand-offs so that conductive elements of the connector are able to be securely mounted onto corresponding solder pads on a printed circuit board.
A ball grid array (BGA) socket includes an insulative member, a number of conductive contacts attached to the insulative member in an array and a number of solder balls respectively attached to corresponding conductive contacts and arranged in an array in accordance with the conductive contacts. The solder balls extend away from a mounting surface of the insulative member for mounting onto corresponding solder pads on a printed circuit board (PCB). The insulative member provides a number of stand-offs on the mounting surface thereof and located in the array of the solder balls. When the BGA socket is located on the PCB and heated, the solder balls become soft or melted and the insulative member sinks until the stand-offs bear against the PCB. Since the stand-offs are located in the array of the solder balls, the solder balls are not spaced from the PCB too close or too far, therefore the solder balls may securely mounted to solder pads on the PCB.
Other objects, advantages and novel features of the invention will become more apparent from the following detailed description of the present embodiment when taken in conjunction with the accompanying drawings.